The present invention relates to a golf ball with high durability and very high resilience.
A method of improving a cover material by adding an inorganic filler (titanium dioxide and barium sulfate) thereto has been proposed, for example, in Japanese Patent Laid-open No. Hei 6-277312. The addition of titanium dioxide and barium sulfate to the cover of a golf ball is effective to give excellent properties such as a carrying performance to the golf ball. With respect to the reason for this, the document describes that the addition of titanium dioxide and barium sulfate to the cover xe2x80x9cshifts a weight distribution in the ball from the core center to the cover side, to increase an inertia moment of the ball, thereby increasing the carry of the golf ballxe2x80x9d.
Such a proposal, however, has been required to be further improved in terms of factors determining golf ball performances, for example, a hardness factor of the cover and core, a composition factor of the cover and core, and a dimple factor. In particular, the ball disclosed in the embodiment of the above proposal has been required to be improved in terms of feeling of hitting the ball and the carry of the ball.
On the other hand, the properties of a golf ball strongly demanded by golf players are generally player""s soft feeling at the time of hitting the ball and the carrying performance of the ball; however, it is regarded as difficult to make both the properties compatible with each other for the following reasons:
(1) If the core is softened for ensuring the player""s soft feeling, a deformed amount of the hit ball becomes large, to degrade the durability against cracking.
(2) If both the core and cover are softened for ensuring both the player""s soft feeling and durability against cracking, the resilience and initial velocity of the ball are reduced, to sacrifice the carrying performance.
(3) If the ball is excessively improved only in terms of the player""s soft feeling, the other properties are sacrificed, to cause such an inconvenience that local deformation of the hit ball becomes large, not to keep the sphericalness of the ball at the initial stage of the carry of the ball, thereby degrading the carrying performance.
To solve the above problems, Japanese Patent Laid-open No. 2000-5341 has proposed an excellent golf ball characterized by combining a core, which is softened to improve the player""s soft feeling and durability against cracking, with a cover to which a reinforcement filler is added.
Such a golf ball, however, has been required to be further improved in terms of resilience.
An object of the present invention is to provide a golf ball with high durability and very high resilience.
As a result of an examination made, by the present inventor, to achieve the above object, it has been found that a golf ball including: a core made from a rubber composition containing polybutadiene as a main rubber component and also an organic sulfur compound; and a cover made from a cover material mainly containing an ionomer resin composed of an Li ion neutralized type ionomer resin and a Mg ion neutralized ionomer resin, and also an inorganic filler having a specific gravity of 3.50 or more; wherein a flexural amount of the core, measured by applying a load of 980 N thereto, is in a range of 4.0 to 5.5 mm; and a specific gravity of the cover material is in a range of 1.020 to 1.110, and a Shore D hardness of the cover is in a range of 55 to 65, is advantageous in improving the productivity and exhibiting excellent properties as described below by a synergism effect of the above-described optimized requirements.
(1) Since the specific gravity of an inorganic filler is optimized, it is possible to improve the durability and prevent degradation of the resilience (carrying performance).
(2) Since an ionomer resin composed of two kinds of ionomer resins of specific metal ion neutralized types is used, it is possible to further improve the resilience (carrying performance) and the carry of the ball.
(3) Since the core is made from a material containing an organic sulfur compound, it is possible to improve the resilience.
The present inventor has further found that the carrying performance of the above-described golf ball is further improved by optimizing dimples of the golf ball as follows:
(4) If a ball is relatively soft, the spin of the hit ball becomes small, and therefor, if the ballistic path of the ball is excessively low, the carry of the ball may become insufficient because of the xe2x80x9cdropxe2x80x9d of the ball. To cope with such an inconvenience, the dimple total volume ratio (VR) is specified, to prevent the xe2x80x9cdropxe2x80x9d of the ball, thereby ensuring a high carrying performance.
The present invention has been accomplished on the basis of the above-described knowledge.
According to the present invention, there is provided a golf ball including: a core made from a rubber composition containing polybutadiene as a main rubber component and also an organic sulfur compound; and a cover made from a cover material mainly containing an ionomer resin composed of an Li ion neutralized type ionomer resin and a Mg ion neutralized ionomer resin, and also an inorganic filler having a specific gravity of 3.50 or more; wherein a flexural amount of the core, measured by applying a load of 980 N thereto, is in a range of 4.0 to 5.5 mm; and a specific gravity of the cover material is in a range of 1.020 to 1.110, and a Shore D hardness of the cover is in a range of 55 to 65.
In the above golf ball, preferably, a flexural amount of the golf ball, measured by applying a load of 980 N thereto, is in a range of 3.2 to 4.5 mm.
The inorganic filler preferably contains at least barium sulfate, and a content of the inorganic filler is in a range of 10 to 25 parts by mass on the basis of 100 parts by mass of the ionomer resin.
A thickness of the cover is preferably in a range of 1.0 to 2.0 mm.
A content of the organic sulfur compound is preferably in a range of 0.05 to 3.00 parts by mass on the basis of 100 parts by mass of the main rubber component.
Further, in the above golf ball, preferably, the golf ball has in the cover surface a large number of dimples; and a dimple total volume ratio (VR) is in a range of 0.85% or less, the dimple total volume ratio being defined as a ratio of a total volume of dimple spaces each of which is present under a plane surface surrounded by an edge portion of the dimple to a total volume of a virtual ball being the same as the golf ball except that the virtual ball has no dimples.